e present work has concentrated primarily on studying the tyrosine kinase tivity of the insulin receptor. In previous studies of a mutant cell line om an insulin resistant patient, a defect in tyrosine kinase activity in e monocytes was demonstrated. A similar defect can be shown in ythrocytes and fibroblasts and repair of this defect in EBV-transformed mphocytes. By contrast, most Type A patients with insulin resistance and w binding have concomitantly low tyrosine kinase activity. A new method s been developed to study red blood cell tyrosine kinase activity of the sulin receptor. A defect in Type II diabetes can be shown. acylglycerol, a phorbol ester, also inhibits insulin binding to cultured lls and blood monocytes. Further, these tumor-promoting agents cause a mplex-type of phosphorylation of the insulin receptor.